An organic light-emitting diode (OLED) display has characteristics including lightness and thinness, a wide viewing angle, low power consumption, a fast response speed and others, and thus receives wide attention. The organic light-emitting diode display, as a new generation of display manners, has begun to gradually replace a traditional liquid crystal display (LCD), and is widely used in a mobile phone screen, a computer monitor, a full-color television, and the like. According to different driving modes, an OLED may be classified into a passive matrix organic light-emitting diode (PMOLED) or an active matrix organic light-emitting diode (AMOLED).
For example, in the AMOLED, a simplest pixel circuit includes two thin film transistors (TFT) having a switching function and a capacitor (C) for storing charges. According to the numbers of the TFTs and the number of the capacitors C, the pixel circuit is briefly referred to as a 2T1C pixel driving circuit, that is, a sub-pixel unit in the AMOLED. Using a pixel circuit diagram with the simplest AMOLED as an example, the pixel driving circuit shown in FIG. 1 is just the 2T1C pixel driving circuit, including a data input switching transistor 1, a driving transistor 2, a storage capacitor 3 and an OLED 4. All TFTs used in FIG. 1 are P-type transistors, Vscan is a scanning voltage, Vdata is a data voltage, VDD is a highest reference voltage of the pixel circuit, and VSS is a lowest reference voltage of the pixel circuit. In an existing display technology, the OLED is loaded with different direct current driving voltages by an external reverse bias voltage device, so that the OLED displays brightness and color as desired at different grayscale values. When the Vscan is a low voltage level, the data input switching transistor 1 is turned on, and the data voltage Vdata is connected to the driving transistor 2, and stored on the storage capacitor 3; a voltage on the storage capacitor 3 causes the driving transistor 2 to remain in a turning-on state all the time, and the driving transistor 2 performs direct current biasing on the OLED 4 all the time. If the OLED 4 is in a direct current biased state for a long time, internal ions are polarized to form a built-in electric field, resulting in a constant increase in a threshold voltage of the OLED 4, and a constant decrease in luminance of the OLED 4, which shortens a service life of the OLED 4. Since direct current bias voltages of the OLED 4 under different grayscales are different, an aging degree of each sub-pixel OLED 4 is different, such that an image displayed on a screen is uneven, which affects a display effect.